feat(wgsl-in): create skeleton for parsing directives

naga/src/front/wgsl/error.rs

@@ -265,6 +265,14 @@ pub(crate) enum Error<'a> {
     PipelineConstantIDValue(Span),
     NotBool(Span),
     ConstAssertFailed(Span),
+    DirectiveNotYetImplemented {
+        kind: &'static str,
+        span: Span,
+        tracking_issue_num: u16,
+    },
+    DirectiveAfterFirstGlobalDecl {
+        directive_span: Span,
+    },
 }
 
 #[derive(Clone, Debug)]
@@ -861,6 +869,41 @@ impl<'a> Error<'a> {
                 labels: vec![(span, "evaluates to false".into())],
                 notes: vec![],
             },
+            Error::DirectiveNotYetImplemented {
+                kind,
+                span,
+                tracking_issue_num,
+            } => ParseError {
+                message: format!("`{kind}` global directives are not yet supported (sorry!)"),
+                labels: vec![(
+                    span,
+                    concat!(
+                        "this directive specifies standard functionality ",
+                        "which is not yet implemented in Naga"
+                    )
+                    .into(),
+                )],
+                notes: vec![format!(
+                    concat!(
+                        "Let Naga maintainers know that you ran into this at ",
+                        "<https://github.com/gfx-rs/wgpu/issues/{}>, ",
+                        "so they can prioritize it!"
+                    ),
+                    tracking_issue_num
+                )],
+            },
+            Error::DirectiveAfterFirstGlobalDecl { directive_span } => ParseError {
+                message: "expected global declaration, but found a global directive".into(),
+                labels: vec![(
+                    directive_span,
+                    "this directive was written after global declaration parsing started".into(),
+                )],
+                notes: vec![concat!(
+                    "global directives are only allowed before global declarations; ",
+                    "maybe hoist this closer to the top of the shader?"
+                )
+                .into()],
+            },
         }
     }
 }

naga/src/front/wgsl/parse/directive.rs

@@ -0,0 +1,41 @@
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+pub enum DirectiveKind {
+    Unimplemented(UnimplementedDirectiveKind),
+}
+
+impl DirectiveKind {
+    pub fn from_ident(s: &str) -> Option<(Self, &'static str)> {
+        Some(match s {
+            "diagnostic" => (
+                Self::Unimplemented(UnimplementedDirectiveKind::Diagnostic),
+                "diagnostic",
+            ),
+            "enable" => (
+                Self::Unimplemented(UnimplementedDirectiveKind::Enable),
+                "enable",
+            ),
+            "requires" => (
+                Self::Unimplemented(UnimplementedDirectiveKind::Requires),
+                "requires",
+            ),
+            _ => return None,
+        })
+    }
+}
+
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+pub enum UnimplementedDirectiveKind {
+    Diagnostic,
+    Enable,
+    Requires,
+}
+
+impl UnimplementedDirectiveKind {
+    pub const fn tracking_issue_num(self) -> u16 {
+        match self {
+            Self::Diagnostic => 5320,
+            Self::Requires => 6350,
+            Self::Enable => 5476,
+        }
+    }
+}

naga/src/front/wgsl/parse/mod.rs

@@ -1,4 +1,5 @@
 use crate::front::wgsl::error::{Error, ExpectedToken};
+use crate::front::wgsl::parse::directive::DirectiveKind;
 use crate::front::wgsl::parse::lexer::{Lexer, Token};
 use crate::front::wgsl::parse::number::Number;
 use crate::front::wgsl::Scalar;
@@ -7,6 +8,7 @@ use crate::{Arena, FastIndexSet, Handle, ShaderStage, Span};
 
 pub mod ast;
 pub mod conv;
+pub mod directive;
 pub mod lexer;
 pub mod number;
 
@@ -136,6 +138,7 @@ enum Rule {
     SingularExpr,
     UnaryExpr,
     GeneralExpr,
+    Directive,
 }
 
 struct ParsedAttribute<T> {
@@ -2357,6 +2360,9 @@ impl Parser {
         let start = lexer.start_byte_offset();
         let kind = match lexer.next() {
             (Token::Separator(';'), _) => None,
+            (Token::Word(word), directive_span) if DirectiveKind::from_ident(word).is_some() => {
+                return Err(Error::DirectiveAfterFirstGlobalDecl { directive_span });
+            }
             (Token::Word("struct"), _) => {
                 let name = lexer.next_ident()?;
 
@@ -2474,6 +2480,29 @@ impl Parser {
 
         let mut lexer = Lexer::new(source);
         let mut tu = ast::TranslationUnit::default();
+
+        // Parse directives.
+        #[allow(clippy::never_loop)]
+        loop {
+            if let Ok(ident) = lexer.peek_ident() {
+                self.push_rule_span(Rule::Directive, &mut lexer);
+                if let Some((kind, name)) = DirectiveKind::from_ident(ident.name) {
+                    match kind {
+                        DirectiveKind::Unimplemented(unimplemented) => {
+                            return Err(Error::DirectiveNotYetImplemented {
+                                kind: name,
+                                span: ident.span,
+                                tracking_issue_num: unimplemented.tracking_issue_num(),
+                            })
+                        }
+                    }
+                }
+                // TODO: add directives to set of expected things in errors later
+                self.pop_rule_span(&lexer);
+            }
+            break;
+        }
+
         loop {
             match self.global_decl(&mut lexer, &mut tu) {
                 Err(error) => return Err(error),